<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
    <body>
        
    
        <button>测试xhr是异步函数</button>
        <script>
          document.querySelector('button').addEventListener('click', function () {
            console.log('1')
    
            const xhr = new XMLHttpRequest()
            xhr.open('post', 'http://ajax-api.itheima.net/api/login')
            xhr.setRequestHeader('content-type', 'application/json')
    
            xhr.addEventListener('load', function () {
              //   console.log(xhr.response)
              //   console.log(JSON.parse(xhr.response))
              console.log('2')
            })
            let obj = {
              username: 'admin',
              password: '123456',
            }
            xhr.send(JSON.stringify(obj))
    
            console.log('3')
          })
        </script>
      </body>
</body>
</html>